Nvidia GTX 960

I have had this problem also.  My GTX 960 would not show up as an option for rendering.  After researching and messing with driver updates.  I installed a program called GPUz .  I use CUP-z for computer/fan/cpu temp info and have done that for years.  Turns out that GUPz is not from the same company however after running GPUz and then starting Premiere Pro CC 2017 it found my 960 and is working fine.  Silly as that sounds, it worked for me.  There are a few threads here on adobe forums that mention this fix. 2017 is running fine and I have my CUDA acceleration back.  All is well in the world again. 

Not everything uses CUDA... read this

http://blogs.adobe.com/premiereprotraining/2011/02/cuda-mercury-playback-engine-and-adobe-premiere-pro.html

Are you using GPU accelerated effects?

Is CUDA enabled in your project settings?

If earlier than Premiere Pro CC, use the CUDA hack:

https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=CUDA+hack&*CUDA hack

If not, tell us your computer specs.